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 * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package javax.xml;

/**
 * Utility class to contain basic XML values as constants.
 *
 * @author Jeff Suttor
 * @see <a href="http://www.w3.org/TR/xml11/">Extensible Markup Language (XML) 1.1</a>
 * @see <a href="http://www.w3.org/TR/REC-xml">Extensible Markup Language (XML) 1.0 (Second
 *     Edition)</a>
 * @see <a href="http://www.w3.org/XML/xml-V10-2e-errata">XML 1.0 Second Edition Specification
 *     Errata</a>
 * @see <a href="http://www.w3.org/TR/xml-names11/">Namespaces in XML 1.1</a>
 * @see <a href="http://www.w3.org/TR/REC-xml-names">Namespaces in XML</a>
 * @see <a href="http://www.w3.org/TR/xmlschema-1/">XML Schema Part 1: Structures</a>
 * @since 1.5
 */
public final class XMLConstants {

  /** Private constructor to prevent instantiation. */
  private XMLConstants() {}

  /**
   * Namespace URI to use to represent that there is no Namespace.
   *
   * <p>Defined by the Namespace specification to be "".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#defaulting">Namespaces in XML, 5.2 Namespace
   *     Defaulting</a>
   */
  public static final String NULL_NS_URI = "";

  /**
   * Prefix to use to represent the default XML Namespace.
   *
   * <p>Defined by the XML specification to be "".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML, 3. Qualified
   *     Names</a>
   */
  public static final String DEFAULT_NS_PREFIX = "";

  /**
   * The official XML Namespace name URI.
   *
   * <p>Defined by the XML specification to be "{@code http://www.w3.org/XML/1998/namespace}".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML, 3. Qualified
   *     Names</a>
   */
  public static final String XML_NS_URI = "http://www.w3.org/XML/1998/namespace";

  /**
   * The official XML Namespace prefix.
   *
   * <p>Defined by the XML specification to be "{@code xml}".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML, 3. Qualified
   *     Names</a>
   */
  public static final String XML_NS_PREFIX = "xml";

  /**
   * The official XML attribute used for specifying XML Namespace declarations, {@link
   * #XMLNS_ATTRIBUTE XMLConstants.XMLNS_ATTRIBUTE}, Namespace name URI.
   *
   * <p>Defined by the XML specification to be "{@code http://www.w3.org/2000/xmlns/}".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML, 3. Qualified
   *     Names</a>
   */
  public static final String XMLNS_ATTRIBUTE_NS_URI = "http://www.w3.org/2000/xmlns/";

  /**
   * The official XML attribute used for specifying XML Namespace declarations.
   *
   * <p>It is <strong><em>NOT</em></strong> valid to use as a prefix. Defined by the XML
   * specification to be "{@code xmlns}".
   *
   * @see <a href="http://www.w3.org/TR/REC-xml-names/#ns-qualnames">Namespaces in XML, 3. Qualified
   *     Names</a>
   */
  public static final String XMLNS_ATTRIBUTE = "xmlns";

  /**
   * W3C XML Schema Namespace URI.
   *
   * <p>Defined to be "{@code http://www.w3.org/2001/XMLSchema}".
   *
   * @see <a href= "http://www.w3.org/TR/xmlschema-1/#Instance_Document_Constructions"> XML Schema
   *     Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated</a>
   */
  public static final String W3C_XML_SCHEMA_NS_URI = "http://www.w3.org/2001/XMLSchema";

  /**
   * W3C XML Schema Instance Namespace URI.
   *
   * <p>Defined to be "{@code http://www.w3.org/2001/XMLSchema-instance}".
   *
   * @see <a href= "http://www.w3.org/TR/xmlschema-1/#Instance_Document_Constructions"> XML Schema
   *     Part 1: Structures, 2.6 Schema-Related Markup in Documents Being Validated</a>
   */
  public static final String W3C_XML_SCHEMA_INSTANCE_NS_URI =
      "http://www.w3.org/2001/XMLSchema-instance";

  /**
   * W3C XPath Datatype Namespace URI.
   *
   * <p>Defined to be "{@code http://www.w3.org/2003/11/xpath-datatypes}".
   *
   * @see <a href="http://www.w3.org/TR/xpath-datamodel">XQuery 1.0 and XPath 2.0 Data Model</a>
   */
  public static final String W3C_XPATH_DATATYPE_NS_URI =
      "http://www.w3.org/2003/11/xpath-datatypes";

  /**
   * XML Document Type Declaration Namespace URI as an arbitrary value.
   *
   * <p>Since not formally defined by any existing standard, arbitrarily define to be "{@code
   * http://www.w3.org/TR/REC-xml}".
   */
  public static final String XML_DTD_NS_URI = "http://www.w3.org/TR/REC-xml";

  /**
   * RELAX NG Namespace URI.
   *
   * <p>Defined to be "{@code http://relaxng.org/ns/structure/1.0}".
   *
   * @see <a href="http://relaxng.org/spec-20011203.html">RELAX NG Specification</a>
   */
  public static final String RELAXNG_NS_URI = "http://relaxng.org/ns/structure/1.0";

  /**
   * Feature for secure processing.
   *
   * <ul>
   *   <li>{@code true} instructs the implementation to process XML securely. This may set limits on
   *       XML constructs to avoid conditions such as denial of service attacks.
   *   <li>{@code false} instructs the implementation to process XML in accordance with the XML
   *       specifications ignoring security issues such as limits on XML constructs to avoid
   *       conditions such as denial of service attacks.
   * </ul>
   */
  public static final String FEATURE_SECURE_PROCESSING =
      "http://javax.xml.XMLConstants/feature/secure-processing";

  /**
   * Property: accessExternalDTD
   *
   * <p>Restrict access to external DTDs and external Entity References to the protocols specified.
   * If access is denied due to the restriction of this property, a runtime exception that is
   * specific to the context is thrown. In the case of {@link javax.xml.parsers.SAXParser} for
   * example, {@link org.xml.sax.SAXException} is thrown.
   *
   * <p><b>Value: </b> a list of protocols separated by comma. A protocol is the scheme portion of a
   * {@link java.net.URI}, or in the case of the JAR protocol, "jar" plus the scheme portion
   * separated by colon. A scheme is defined as:
   *
   * <blockquote>
   *
   * scheme = alpha *( alpha | digit | "+" | "-" | "." )<br>
   * where alpha = a-z and A-Z.<br>
   * <br>
   * And the JAR protocol:<br>
   * jar[:scheme]<br>
   * <br>
   * Protocols including the keyword "jar" are case-insensitive. Any whitespaces as defined by
   * {@link java.lang.Character#isSpaceChar } in the value will be ignored. Examples of protocols
   * are file, http, jar:file.
   *
   * </blockquote>
   *
   * <p><b>Default value:</b> The default value is implementation specific and therefore not
   * specified. The following options are provided for consideration:
   *
   * <blockquote>
   *
   * <UL>
   *   <LI>an empty string to deny all access to external references;
   *   <LI>a specific protocol, such as file, to give permission to only the protocol;
   *   <LI>the keyword "all" to grant permission to all protocols.
   * </UL>
   *
   * <br>
   * When FEATURE_SECURE_PROCESSING is enabled, it is recommended that implementations restrict
   * external connections by default, though this may cause problems for applications that process
   * XML/XSD/XSL with external references.
   *
   * </blockquote>
   *
   * <p><b>Granting all access:</b> the keyword "all" grants permission to all protocols.
   *
   * <p><b>System Property:</b> The value of this property can be set or overridden by system
   * property {@code javax.xml.accessExternalDTD}.
   *
   * <p><b>jaxp.properties:</b> This configuration file is in standard {@link java.util.Properties}
   * format and typically located in the {@code conf} directory of the Java installation. If the
   * file exists and the system property is specified, its value will be used to override the
   * default of the property.
   *
   * @since 1.7
   */
  public static final String ACCESS_EXTERNAL_DTD =
      "http://javax.xml.XMLConstants/property/accessExternalDTD";

  /**
   * Property: accessExternalSchema
   *
   * <p>Restrict access to the protocols specified for external reference set by the schemaLocation
   * attribute, Import and Include element. If access is denied due to the restriction of this
   * property, a runtime exception that is specific to the context is thrown. In the case of {@link
   * javax.xml.validation.SchemaFactory} for example, org.xml.sax.SAXException is thrown.
   *
   * <p><b>Value:</b> a list of protocols separated by comma. A protocol is the scheme portion of a
   * {@link java.net.URI}, or in the case of the JAR protocol, "jar" plus the scheme portion
   * separated by colon. A scheme is defined as:
   *
   * <blockquote>
   *
   * scheme = alpha *( alpha | digit | "+" | "-" | "." )<br>
   * where alpha = a-z and A-Z.<br>
   * <br>
   * And the JAR protocol:<br>
   * jar[:scheme]<br>
   * <br>
   * Protocols including the keyword "jar" are case-insensitive. Any whitespaces as defined by
   * {@link java.lang.Character#isSpaceChar } in the value will be ignored. Examples of protocols
   * are file, http, jar:file.
   *
   * </blockquote>
   *
   * <p><b>Default value:</b> The default value is implementation specific and therefore not
   * specified. The following options are provided for consideration:
   *
   * <blockquote>
   *
   * <UL>
   *   <LI>an empty string to deny all access to external references;
   *   <LI>a specific protocol, such as file, to give permission to only the protocol;
   *   <LI>the keyword "all" to grant permission to all protocols.
   * </UL>
   *
   * <br>
   * When FEATURE_SECURE_PROCESSING is enabled, it is recommended that implementations restrict
   * external connections by default, though this may cause problems for applications that process
   * XML/XSD/XSL with external references.
   *
   * </blockquote>
   *
   * <p><b>Granting all access:</b> the keyword "all" grants permission to all protocols.
   *
   * <p><b>System Property:</b> The value of this property can be set or overridden by system
   * property {@code javax.xml.accessExternalSchema}
   *
   * <p><b>jaxp.properties:</b> This configuration file is in standard {@link java.util.Properties}
   * format and typically located in the {@code conf} directory of the Java installation. If the
   * file exists and the system property is specified, its value will be used to override the
   * default of the property.
   *
   * @since 1.7
   */
  public static final String ACCESS_EXTERNAL_SCHEMA =
      "http://javax.xml.XMLConstants/property/accessExternalSchema";

  /**
   * Property: accessExternalStylesheet
   *
   * <p>Restrict access to the protocols specified for external references set by the stylesheet
   * processing instruction, Import and Include element, and document function. If access is denied
   * due to the restriction of this property, a runtime exception that is specific to the context is
   * thrown. In the case of constructing new {@link javax.xml.transform.Transformer} for example,
   * {@link javax.xml.transform.TransformerConfigurationException} will be thrown by the {@link
   * javax.xml.transform.TransformerFactory}.
   *
   * <p><b>Value:</b> a list of protocols separated by comma. A protocol is the scheme portion of a
   * {@link java.net.URI}, or in the case of the JAR protocol, "jar" plus the scheme portion
   * separated by colon. A scheme is defined as:
   *
   * <blockquote>
   *
   * scheme = alpha *( alpha | digit | "+" | "-" | "." )<br>
   * where alpha = a-z and A-Z.<br>
   * <br>
   * And the JAR protocol:<br>
   * jar[:scheme]<br>
   * <br>
   * Protocols including the keyword "jar" are case-insensitive. Any whitespaces as defined by
   * {@link java.lang.Character#isSpaceChar } in the value will be ignored. Examples of protocols
   * are file, http, jar:file.
   *
   * </blockquote>
   *
   * <p><b>Default value:</b> The default value is implementation specific and therefore not
   * specified. The following options are provided for consideration:
   *
   * <blockquote>
   *
   * <UL>
   *   <LI>an empty string to deny all access to external references;
   *   <LI>a specific protocol, such as file, to give permission to only the protocol;
   *   <LI>the keyword "all" to grant permission to all protocols.
   * </UL>
   *
   * <br>
   * When FEATURE_SECURE_PROCESSING is enabled, it is recommended that implementations restrict
   * external connections by default, though this may cause problems for applications that process
   * XML/XSD/XSL with external references.
   *
   * </blockquote>
   *
   * <p><b>Granting all access:</b> the keyword "all" grants permission to all protocols.
   *
   * <p><b>System Property:</b> The value of this property can be set or overridden by system
   * property {@code javax.xml.accessExternalStylesheet}
   *
   * <p><b>jaxp.properties:</b> This configuration file is in standard {@link java.util.Properties}
   * format and typically located in the {@code conf} directory of the Java installation. If the
   * file exists and the system property is specified, its value will be used to override the
   * default of the property.
   *
   * @since 1.7
   */
  public static final String ACCESS_EXTERNAL_STYLESHEET =
      "http://javax.xml.XMLConstants/property/accessExternalStylesheet";

  /**
   * Feature: useCatalog
   *
   * <p>Instructs XML processors to use XML Catalogs to resolve entity references. Catalogs may be
   * set through JAXP factories, system properties, or jaxp.properties by using the {@code
   * javax.xml.catalog.files} property defined in {@link javax.xml.catalog.CatalogFeatures}. The
   * following code enables Catalog on SAX parser:
   *
   * <pre>{@code
   * SAXParserFactory spf = SAXParserFactory.newInstance();
   * spf.setFeature(XMLConstants.USE_CATALOG, true);
   * SAXParser parser = spf.newSAXParser();
   * parser.setProperty(CatalogFeatures.Feature.FILES.getPropertyName(), "catalog.xml");
   * }</pre>
   *
   * <p><b>Value:</b> a boolean. If the value is true, and a catalog is set, the XML parser will
   * resolve external references using {@link javax.xml.catalog.CatalogResolver}. If the value is
   * false, XML Catalog is ignored even if one is set. The default value is true.
   *
   * <p><b>System Property:</b> The value of this property can be set or overridden by system
   * property {@code javax.xml.useCatalog}
   *
   * <p><b>jaxp.properties:</b> This configuration file is in standard {@link java.util.Properties}
   * format and typically located in the {@code conf} directory of the Java installation. If the
   * file exists and the system property is specified, its value will be used to override the
   * default value of the property.
   *
   * @since 9
   */
  public static final String USE_CATALOG = "http://javax.xml.XMLConstants/feature/useCatalog";
}
